Vulnerability Database

328,409

Total vulnerabilities in the database

CVE-2020-9054

Multiple ZyXEL network-attached storage (NAS) devices running firmware version 5.21 contain a pre-authentication command injection vulnerability, which may allow a remote, unauthenticated attacker to execute arbitrary code on a vulnerable device. ZyXEL NAS devices achieve authentication by using the weblogin.cgi CGI executable. This program fails to properly sanitize the username parameter that is passed to it. If the username parameter contains certain characters, it can allow command injection with the privileges of the web server that runs on the ZyXEL device. Although the web server does not run as the root user, ZyXEL devices include a setuid utility that can be leveraged to run any command with root privileges. As such, it should be assumed that exploitation of this vulnerability can lead to remote code execution with root privileges. By sending a specially-crafted HTTP POST or GET request to a vulnerable ZyXEL device, a remote, unauthenticated attacker may be able to execute arbitrary code on the device. This may happen by directly connecting to a device if it is directly exposed to an attacker. However, there are ways to trigger such crafted requests even if an attacker does not have direct connectivity to a vulnerable devices. For example, simply visiting a website can result in the compromise of any ZyXEL device that is reachable from the client system. Affected products include: NAS326 before firmware V5.21(AAZF.7)C0 NAS520 before firmware V5.21(AASZ.3)C0 NAS540 before firmware V5.21(AATB.4)C0 NAS542 before firmware V5.21(ABAG.4)C0 ZyXEL has made firmware updates available for NAS326, NAS520, NAS540, and NAS542 devices. Affected models that are end-of-support: NSA210, NSA220, NSA220+, NSA221, NSA310, NSA310S, NSA320, NSA320S, NSA325 and NSA325v2

  • Published: Mar 4, 2020
  • Updated: Nov 9, 2025
  • CVE: CVE-2020-9054
  • Severity: Critical
  • Exploit:

CVSS v3:

  • Severity: Critical
  • Score: 9.8
  • AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CVSS v2:

  • Severity: High
  • Score: 10
  • AV:N/AC:L/Au:N/C:C/I:C/A:C

CWEs:

OWASP TOP 10:

Software From Fixed in
zyxel / nas326_firmware - 5.21\(aazf.7\)c0
zyxel / nas520_firmware - 5.21\(aasz.3\)c0
zyxel / nas540_firmware - 5.21\(aatb.4\)c0
zyxel / nas542_firmware - 5.21\(abag.4\)c0
zyxel / atp100_firmware 4.35 4.35\(abps.3\)c0
zyxel / atp200_firmware 4.35 4.35\(abfw.3\)c0
zyxel / atp500_firmware 4.35 4.35\(abfu.3\)c0
zyxel / atp800_firmware 4.35 4.35\(abiq.3\)c0
zyxel / usg20-vpn_firmware 4.35 4.35\(abaq.3\)c0
zyxel / usg20w-vpn_firmware 4.35 4.35\(abar.3\)c0
zyxel / usg40_firmware 4.35 4.35\(aala.3\)c0
zyxel / usg40w_firmware 4.35 4.35\(aalb.3\)c0
zyxel / usg60_firmware 4.35 4.35\(aaky.3\)c0
zyxel / usg60w_firmware 4.35 4.35\(aakz.3\)c0
zyxel / usg110_firmware 4.35 4.35\(aaph.3\)c0
zyxel / usg210_firmware 4.35 4.35\(aapi.3\)c0
zyxel / usg310_firmware 4.35 4.35\(aapj.3\)c0
zyxel / usg1100_firmware 4.35 4.35\(aapk.3\)c0
zyxel / usg1900_firmware 4.35 4.35\(aapl.3\)c0
zyxel / usg2200_firmware 4.35 4.35\(abae.3\)c0
zyxel / vpn50_firmware 4.35 4.35\(abhl.3\)c0
zyxel / vpn100_firmware 4.35 4.35\(abfv.3\)c0
zyxel / vpn300_firmware 4.35 4.35\(abfc.3\)c0
zyxel / vpn1000_firmware 4.35 4.35\(abip.3\)c0
zyxel / zywall110_firmware 4.35 4.35\(aaaa.3\)c0
zyxel / zywall310_firmware 4.35 4.35\(aaab.3\)c0
zyxel / zywall1100_firmware 4.35 4.35\(aaac.3\)c0

Frequently Asked Questions

A security vulnerability is a weakness in software, hardware, or configuration that can be exploited to compromise confidentiality, integrity, or availability. Many vulnerabilities are tracked as CVEs (Common Vulnerabilities and Exposures), which provide a standardized identifier so teams can coordinate patching, mitigation, and risk assessment across tools and vendors.

CVSS (Common Vulnerability Scoring System) estimates technical severity, but it doesn't automatically equal business risk. Prioritize using context like internet exposure, affected asset criticality, known exploitation (proof-of-concept or in-the-wild), and whether compensating controls exist. A "Medium" CVSS on an exposed, production system can be more urgent than a "Critical" on an isolated, non-production host.

A vulnerability is the underlying weakness. An exploit is the method or code used to take advantage of it. A zero-day is a vulnerability that is unknown to the vendor or has no publicly available fix when attackers begin using it. In practice, risk increases sharply when exploitation becomes reliable or widespread.

Recurring findings usually come from incomplete Asset Discovery, inconsistent patch management, inherited images, and configuration drift. In modern environments, you also need to watch the software supply chain: dependencies, containers, build pipelines, and third-party services can reintroduce the same weakness even after you patch a single host. Unknown or unmanaged assets (often called Shadow IT) are a common reason the same issues resurface.

Use a simple, repeatable triage model: focus first on externally exposed assets, high-value systems (identity, VPN, email, production), vulnerabilities with known exploits, and issues that enable remote code execution or privilege escalation. Then enforce patch SLAs and track progress using consistent metrics so remediation is steady, not reactive.

SynScan combines attack surface monitoring and continuous security auditing to keep your inventory current, flag high-impact vulnerabilities early, and help you turn raw findings into a practical remediation plan.